Characterization of porosity of laser welded joints

Magistrsko delo opisuje proces karakterizacije poroznosti lasersko zavarjenih spojev. Karakterizacijo zvarnih spojev iz nerjavnega jekla sem izvajal z namenom optimizacije pulznega laserskega varjenja prekrovnega zvarnega spoja. Obravnavani zvarni spoj je zaradi kombinacije uporabljenega materiala, geometrije zvarnega spoja in neustreznih parametrov varjenja močno porozen. Na nastanek poroznosti pri pulznem laserskem varjenju lahko vplivamo z obliko laserskega pulza. V magistrskem delu smo uporabili dve obliki žagastega pulza. Med eksperimentiranjem smo spreminjali tudi moč laserskega žarka. Zvarne spoje smo vrednotili glede na strižno trdnost, globino prevaritve, temperature varjencev med varjenjem in glede na delež poroznosti. Poroznost je zelo pogosta napaka laserskih zvarov, poleg tega pa je tudi vrednotenje poroznosti zahtevnejše. V ta namen smo v programskem okolju MATLAB razvili zelo natančen merilni sistem za 2 D-vrednotenje poroznosti. Razviti merilni sistem je bil zasnovan z namenom hitrega in cenovno ugodnega vrednotenja deleža poroznosti na osnovi rentgenskih slik. Razviti merilni sistem nam je omogočil določitev optimalnih varilnih parametrov. Pri optimiranih parametrih zvarni spoj izpolnjuje zahteve zvarnega spoja, po strižni trdnosti, temperaturni obremenitvi zvarnega mesta in deležu poroznosti zvarnega spoja.Master thesis presents characterization of porosity in weld made with laser welding. The characterization was done for pulsed laser welding of stainless steel in a lap joint. The produced laser welds were very porous due to improper weld geometry, used material and unsuitable welding parameters. It is known that the shape of the laser pulse effects on the weld porosity. The experiments were planned in order to lower the level of porosity by changing the laser power and by the use of saw-like pulses. The welds were characterized by the shear test, laser weld penetration, the temperature of the workpiece during welding and weld porosity. Weld porosity is very frequent defect, while its determination is very difficult. The computer code was developed in MATLAB environment and it enables a precise measurement of 2D porosity. A simple system has been developed for fast determination of porosity, using a radiographical images. The developed system enables determination of optimal welding parameters in which the welding joint meet demands of the suitably shear strength, temperature load and weld porosity